Recently, multi-function peripheral device is popular for digital image processing. It provides functions for image scanning and printing. In Multi-function peripheral device, graphic and text separation and text enhancement are often processed in Multi-function peripheral device.
Document usually comprises a graphic part and a text part. By way of graphic and text separation processing, the graphic part and the text part can be separated for further processing. For example, in case of without graphic/text separation process, when printing a document, printers use color ink to print the whole content. That is, the text part will be printed with color ink as well and therefore wastes color ink. However, in case of having graphic and text separation process, the graphic part is printed with color ink and the text part is printed with black ink and therefore the color ink is saved.
The graphic and text separation methods of prior art comprise a hue adjusting method, an edge detecting method and a chroma and luminance detecting method. These prior art methods do not classify the image according to text and graphic, but apply a single process on the whole image. It won't provide a good graphic and text separation result without classifying the image according to graphic and text. For example, the hue adjusting method adjusts the hue of the whole image, such as increasing the hue of the brighter part of the image and reducing the hue of the darker part of the image, to separate graphic and text. Because graphics and texts are subjected to the same process of hue adjusting, it will impact the hue of the whole image.
Besides, the edge enhancement method often incorrectly recognized the noise and graphics of the image of document as texts and therefore generated error recognition result. However, applying the method which used chroma and luminance to separate text and graphic on low or zero chroma photos will also fault the result.
The purpose of text enhancement is to make the image of text clearer. The prior art methods for text enhancement do not separate text and graphic before the text enhancement process, but adjust the luminance of the whole image to clear the text image. However, such adjustment will decrease the hue of the graphics of the document.